The suspect, a 35-year-old Dutch citizen, traveled around Spain in a van he used as a mobile office, Spain's National Police said in a statement Sunday.

Police arrested him Thursday north of Barcelona, Spain, on a European arrest warrant at the request of judicial authorities in the Netherlands, the statement said.

Authorities have not released his name, and a photo police issued showing his detention blurred his face.

The arrest comes a month after Internet users around the globe faced slowed-down service during the prolonged denial-of-service assault on The Spamhaus Project, a European spam-fighting group.

Security experts said the attack used more sophisticated techniques than most distributed denial of service, or DDoS, attacks and targeted the Web's infrastructure, which led to other sites performing slowly.

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In a DDoS attack, computers flood a website with requests, overwhelming its servers and causing it to crash or become inaccessible for many users.

Last month's attack appears to be part of a fierce feud between organizations that monitor spam and try to block it and companies that accuse spam blockers of unjustly blacklisting them.

The Spamhaus Project is a nonprofit that patrols the Internet for spammers and publishes a list of Web servers those spammers use.

Matthew Prince, CEO of Internet security firm CloudFlare, estimates the group may be responsible for up to 80% of all spam that gets blocked.

And last month, the group added a new name to its blacklist, CyberBunker, and said spammers use the company as a host to spray junk mail across the Web.

During his arrest, the suspect told authorities he was a diplomat and "minister of telecommunications and foreign relations of the Republic of CyberBunker," police said Sunday.

Last month CyberBunker -- a Dutch company housed in a former NATO nuclear bunker -- did not take credit for the attack against Spamhaus but didn't shy away from talking about it.

"This here is the Internet community puking out Spamhaus," Sven Olaf Kamphuis of CyberBunker told CNN in March. "We've had it with the guys. ... What we see right here is the Internet puking out a cancer."

Kamphuis and other critics say that Spamhaus oversteps its bounds and has essentially destroyed innocent websites in its spam-fighting efforts.

"Spamhaus itself is a more urgent danger" than spam, Kamphuis told CNN. "Pointing at websites and saying they want it shut down and then they get it shut down without any court order. That is a significantly larger threat to internet and freedom of speech and net neutrality than anything else."

In a statement Friday, Spamhaus thanked Dutch authorities for last week's arrest.

"Spamhaus will resolutely continue its mission to provide reliable protection against cyberthreats such as spam, malware and botnets and work with Internet service providers and organizations worldwide to create a safer Internet," the organization said in a statement.